Optical disc and method for reproducing the same

ABSTRACT

The present invention provides a technique for improving reliability of reading header information. The optical disk is composed of a recording track. The recording track includes a data recording region in which recording pits are formed for recording data, and a header region in which pre-pits are formed for recording header information identifying said data recording region. Said recording pits have a reflectance smaller than that of a space in which said recording pits are not formed. Said recording pits and said pre-pits are formed so that an amplitude (dynamic range) of a level of an optical signal reflected from said header regions is larger than that of an optical signal reflected from said data recording regions.

TECHNICAL FIELD

The present invention is related to optical recording media and methodsof reading the same, more particularly to recordable or rewritableoptical recording media and methods of reading the same.

BACKGROUND ART

Recordable or rewritable optical disks have now become popular. CD-Rs(Compact Disc Recordable) and CD-RWs (Compact Disc Rewritable) aretypical recordable or rewritable optical disks. In recent years, DVD-Rs(Digital Versatile Disk) and DVD-RWs (DVD ReWritable), which haverecording capacities larger than CD-Rs and CD-RWs, are commerciallyavailable.

Recording data onto recordable optical disks is often achieved by phasechange recording. Phase change recording involves partially changing arecording layer made of phase change recording material in qualitythrough irradiating a laser beam, and thereby forming recording pitsthereon. Irradiating a laser beam increases the temperature of theirradiated portions. The temperature increase changes the irradiatedportions in quality, and thereby alters the reflectance of theirradiated portions. The irradiated portions, with their reflectancesaltered, are used as recording pits. The reflectances of the irradiatedportions may be decreased or increased.

Phase change recording designed to decrease the reflectance of recordingpits is preferable from the viewpoint of the compatibility betweenrecordable optical disks and read-only optical disks (namely, CD-ROMs).CD-ROMs is designed to record data thereon by using pre-pits, whosereflectances are reduced by embossing. Recording pits on recordableoptical disks, which have reduced reflectances, exhibit the same effectas the pre-pits on CD-ROMs. Therefore, recordable optical disks can bedesigned so as to have the compatibility with the read only opticaldisks (namely, CD-ROMs).

Phase change recording designed to increase the reflectance of recordingpits, on the other hand, is advantageous for improving an S/N ratio ofan optical signal reflected by optical disks. In most recordable opticaldisks, the size of the region where recording pits are formed is largerthan that of a space (namely, the portions except the region whererecording pits are formed) Optical disks that have the decreasedreflectance in the space and the increased reflectance in the recordingpits reduce the average of levels of reflected light beams, and therebyeffectively improve the S/N ratio. The improvement in the S/N ratio iscommercially desirable because the improvement of the S/N ratio allowsthe improvement of the recording density, namely, the increase in theamount of recordable data for a single optical disk.

FIG. 1 is a plan view of an optical disk 101 for phase change recordingdesigned to increase the reflectance of recording pits. A spiralrecording track 104 is formed on the optical disk 101. The recordingtrack 104 is divided into sectors each having a predetermined sectorlength. Each sector contains header information (or format information)including the sector address at the head portion. The portions where theheader information is recorded are referred to as header regions 105.User data are recorded in the remaining portions of the sectors. Theportions where the user data are recorded are referred to as datarecording regions 106.

FIG. 2 shows the cross sectional structure of the optical disk 101. Theoptical disk 101 includes a transparent substrate 103 and a recordinglayer 102 covering the transparent substrate 103. The recording layer102 is made of phase change recording material which has a reducedreflectance in the crystalline phase compared to that in the amorphousphase.

The data recording regions 106 are provided with recording pits 111corresponding to the user data in the recording layer 102. A light beamused for data reproduction is transmitted across the transparentsubstrate 103 to reach the recording layer 102, and is reflected by therecording layer 102. A solid line in FIG. 1 indicates the reflection ofthe light beam by a recording pit 111, and a broken line indicates thereflection of the light beam by a space 112 of the recording layer 102.

The recording pit 111 is the portion exhibiting the amorphous phasewithin the recording layer 102, and the space 112 is the portionexhibiting the crystalline phase. This configuration makes thereflectance in the recording bit 111 higher than the reflectance in thespace 112.

Such design of the recording layer 102 effectively improves the S/Nratio. The crystalline portion of the recording layer 102 exhibitsminute non-uniformity over the area, because the crystalline portion ofthe recording layer 102 is formed of a group of micro crystals. Theminute non-uniformity in the reflectance causes noise. The amorphousportion, on the other hand, exhibits reduced noise. The configuration inwhich the reflectance of the amorphous portion is high and thereflectance of the crystalline portion is low reduces the level of thelight reflected from the portion that causes large noise, and therebyimproves the S/N ratio.

The header regions 105 are provided with pre-pits corresponding to theheader information. Embossed patterns are formed inside the pre-pits.The embossed patterns reduce the reflectance of the pre-pits below thatof the remaining portions of the header regions 105.

One problem of such phase change recording is the reliability in readingout the header information. The optical disk 101 for the phase changerecording designed to increase the reflectance of the recording pitshave the header region 105 formed within the crystalline portion of therecording layer 102 (namely, the portion where the reflectance is low).The decrease in the reflectance of the header region 105 furtherdecreases the reflectance of the pre-pits formed in the header region105. This may reduce the level of the optical signal reflected from theheader region 105, and reduce the reliability in reading out the headerinformation. FIG. 3 is an example of an eye-pattern of reproducedsignals obtained from the optical signals reflected from the headerregion 105 and the data recording region 106. The reproduced signals areobtained by converting the optical signals into electric signals,cutting the direct current components of the electric signals, andextracting only the alternating current components. As indicated by theeye-pattern, the amplitude of the level of the reproduced signalobtained from the header region 105 is smaller than that of thereproduced signal obtained from the data recording region 106. Thisdeteriorates the reliability in reading the header information writtenin the header region 105.

The header information (or format information) can be recorded in awobble groove for tracking, instead of the pre-pits. Recording headerinformation onto the wobble groove is achieved by modulating the wobblepattern of the wobble groove in response to the header information. Thismethod is referred to as a wobble modulation and applied to CD-Rs.However, the wobble modulation intrinsically exhibits a reduced S/Nratio since the amplitude of the wobble pattern is limited. Moreover,the reduction in the S/N ratio is severe for the phase change recordingdesigned to increase the reflectance of recording pits, because thisrequires forming the wobble groove in the crystalline portion (namely,the portion where the reflectance is low).

A technique for improving the reliability in reading out the headerinformation is disclosed in Japanese Laid Open Patent Application (JP-ANo. P2000-311343A). This document discloses a technique of increasingthe reproduction amplitude of an address signal (namely, headerinformation) by controlling a disk drive so as to make the level of thelight beam used for the reproduction of an address region (namely, aheader region) stronger than that of a data region (namely, a datarecording region).

Additionally, a technique of improving the degree of the modulation ofpre-pit portions is disclosed in Japanese Laid Open Patent Application(JP-A No. P2000-339690A). This document discloses a technique thatimproves the modulation degree through irradiating a laser beam onpre-pit portions within the recording layer during manufacture so thatthe pre-pit portions are changed into the recorded state.

DISCLOSURE OF INVENTION

The present invention provides a technique for improving the reliabilityin reading out header information. Especially, the present inventionprovides a technique for improving the reliability in reading out theheader information through adopting improved optical disk structure.

In one aspect of the present invention, an optical disk is composed of arecording track. The recording track includes data recording regions inwhich recording pits are formed for recording data, and header regionsin which pre-pits are formed for recording header informationidentifying said data recording regions. Said recording pits have areflectance larger than that of a space in which said recording pits arenot formed. Said recording pits and said pre-pits are formed so that anamplitude (dynamic range) of a level of an optical signal reflected fromsaid header regions is larger than that of an optical signal reflectedfrom said data recording regions.

In order to increase the amplitude of the level of the optical signalreflected from said header regions above that of the level of theoptical signal reflected from said data recording regions, thereflectance of the recording layer may be appropriately adjusted. Indetail, reflectances of said recording pits within said data recordingregions, said space within said data recording regions, said pre-pitswithin said header regions, and a space within said header regions,where said pre-pits are not formed, may be adjusted so that, whenoptical beams having the same intensity are irradiated on said datarecording regions and said header regions, an amplitude of a level of anoptical signal reflected by said header regions is equal to or largerthan that of a level of an optical signal reflected by said datarecording regions.

Alternatively, the pre-pits may be deeply formed. When said datarecording regions include a pregroove in which said recording pits areformed, a depth of said pre-pits is preferably deeper than that of saidpregroove; it would be most preferable that the depth of said pre-pitsis twice as deep as that of said pregroove.

The recording pits and pre-pits thus constructed effectively reduceerrors during detection of the header information recorded as thepre-pits.

In another aspect of the present invention, an optical disk is composedof a recording track including

-   -   data recording regions where recording pits are formed for        recording data, and header regions where pre-pits are formed for        recording header information identifying said data recording        regions. Said recording pits have a reflectance larger than that        of a space, where said recording pits are not formed. Said        recording pits and said pre-pits are formed so that a signal        modulation degree of said header regions is larger than that of        said data recording regions. The signal modulation degrees of        said header and data recording regions are obtained by dividing        the amplitudes of the levels of the optical signals obtained        from the respective regions for the case when the optical        signals exhibits the maximum repetition rate by the amplitudes        of the levels of the optical signals for the case when the        optical signals exhibits the minimum repetition rate. Increasing        the signal modulation degree of said header regions above that        of said data recording regions improves the S/N ratio of the        optical signal reflected from the optical disk, as a whole, and        thus effectively improves the reliability of the detection of        the header information.

The increase in the signal modulation degree of said header regionsabove that of said data recording regions may be achieved throughreducing the linear recording density of said header regions below thatof the data recording regions.

When the linear recording density of said header regions is configuredto be larger than that of said data recording regions, said recordingpits and said pre-pits are preferably formed so that the cycle of thechannel clock reproduced from said header regions is n-times as long asthat of the channel clock reproduced from said data recording regions.The fact that the linear recording density of said header regions islarger than that of said data recording regions results in thedifference in the cycle of the channel clock. Successively reading datafrom regions exhibiting different cycles of the channel clocks requirestime for the synchronization of the clocks; this may cause time when nodata can be reproduced from the regions. Configuring the cycle of thechannel clock reproduced from said header regions to be n-times as largeas that of the channel clock reproduced from said data recording regionsfacilitates the channel clock synchronization.

When said data recording regions are provided with a wobble groove inwhich said recording pits are formed, it would be preferable if saidpre-pits and said wobble groove are formed so that the cycle of thechannel clock reproduced from said header regions to be n-times as largeas that of the channel clock reproduced from said data recordingregions.

In still another aspect of the present invention, an optical disk iscomposed of a recording track, the recording track includes datarecording regions where recording pits are formed for recording data,and header regions where pre-pits are formed for recording headerinformation identifying said data recording regions. Said recording pitshave a reflectance larger than that of a space, where said recordingpits are not formed. One of said pre-pits, which is located closest tohead of said header regions, has a longer length than the maximum pitlength defined by a standard for coding said data. The long pre-pitallows clearly detecting the header regions.

Said header regions may be collectively formed in a leading portion ofsaid recording track disposed in an inner circumference region of saidoptical disk.

An optical disk reading method in accordance with the present inventionis composed of a step of providing a drive including a signalreproducing circuit with the aforementioned optical disk, and a step ofconfiguring characteristics of said signal reproducing circuit forreading said header information recorded in said header regions so thatsaid configured characteristics are different from characteristics usedfor reading data recorded in said data recording regions. This opticaldisk reading method allows optimizing the characteristics of the signalreproducing circuit for the header regions. The combination of theoptimization of the characteristics of the signal reproducing circuitand the optimization of the structure of the optical disk furtherimproves the reliability of the detection of the header information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of a conventional optical disk;

FIG. 2 is a sectional view of the conventional optical disk;

FIG. 3 shows respective eye-patterns of reproduced signals obtained fromheader regions and data recording regions of the conventional opticaldisk;

FIG. 4 is a plan view showing embodiments of an optical disk accordingto the present invention;

FIG. 5 is a sectional view showing the embodiments of the optical diskaccording to the present invention;

FIG. 6 shows an enlarged view of a recording track in first and secondembodiments and an intensity of an optical signal obtained from therecording track;

FIG. 7 shows an eye-pattern of a reproduced signal obtained from therecording track;

FIG. 8 shows an eye-pattern of a reproduced signal obtained from therecording track;

FIG. 9 shows an enlarged view of a recording track in a third embodimentand an intensity of an optical signal obtained from the recording track;

FIG. 10 is a plan view showing a modification of the third embodiment;

FIG. 11 is a plan view showing another modification of the thirdembodiment; and

FIG. 12 is a plan view showing still another modification in the thirdembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

An optical disk 1 in a first embodiment of the present invention iscomposed of a spirally formed recording track 4, as shown in FIG. 4. Therecording track 4 is divided into sectors having a predetermined sectorlength. Each of the sectors includes a header region 5 and a datarecording region 6. The header regions 5 are located at the head of thesectors, and the data recording regions 6 are circumferentially adjacentto the header regions 5. Header information including a sector addressis recorded in the header regions 5, and user data is recorded in thedata recording regions 6.

FIG. 5 shows the cross sectional structure of the optical disk 1. Theoptical disk 1 includes a transparent substrate 3 and a recording layer2 covering the transparent substrate 3. The transparent substrate 3 istypically made of polymer plastic such as poly-carbonate and poly-methylmethacrylate. The recording layer 2 is made of phase change recordingmaterial which has the reflectance in the amorphous phase higher thanthe reflectance in the crystalline phase. The recording layer 2typically includes a first ZnS—SiO₂ film, a Ge₂Sb₂Te₅ film, a secondZnS—SiO₂ film, and an Al—Ti film, which are sequentially laminated onthe transparent substrate 3. The film thicknesses of the first ZnS—SiO₂film, the Ge₂Sb₂Te₅ film, the second ZnS—SiO₂ film and the Al—Ti filmare 125 nm, 13 nm, 50 nm, and 200 nm, respectively. Forming the firstZnS—SiO₂ film to be sufficiently thick on the transparent substrate 3allows the reflectance of the amorphous phase to be higher than thereflectance of the crystalline phase.

FIG. 6 is an enlarged view of the recording track 4. A pregroove 10 usedfor tracking is formed in the data recording regions 6. Recording pits11 for recording the user data is formed inside the pregroove 10.

In the portions of the data recording regions 6 where the recording pits11 are formed, the recording layer 2 is made amorphous, while therecording layer 2 is made crystalline in the remaining portion. Thereflectance in the recording pits 11 is high due to the high reflectanceof the amorphous portion of the recording layer 2. On the other hand,the portion (space) except the recording pits 11, which is referred toas a space, is crystalline in the data recording regions 6, and thisreduces the reflectance in the space of the data recording regions 6.Forming the pregroove 10 reduces the reflectance in the spaces of thedata recording regions 6 below the intrinsic reflectance of thecrystalline phase of the recording layer 2. In FIG. 6, the level of theoptical signal reflected from the data recording regions 6 is indicatedby an arrow 13.

Pre-pits 12 are formed in the header regions 5. In the recording layer2, the spaces of the header regions 5 (namely, the portion where thepre-pits 12 are not formed) are in the crystalline phase. Therefore, thespaces of the header regions 5 have the intrinsic reflectance of thecrystal phase of the recording layer 2. On the other hand, embossedpatterns are formed inside the pre-pits 12. The embossed patternsdecrease the reflectance of the pre-pits 12 through interference. Hence,the pre-pits 12 have the reflectance lower than the spaces of the headerregions 5.

Therefore, the recording pits 11 formed in the data recording regions 6have the highest reflectance, and the spaces of the header regions 5have the second highest reflectance. The spaces of the data recordingregions 6 have the third highest reflectance, and the pre-pits 12 formedin the header regions 5 have the lowest reflectance. Hence, as shown inFIG. 6, the level of the optical signal reflected from the recordingpits 11 formed in the data recording regions 6 is the highest, and thelevel of the optical signal reflected from the spaces of the headerregions 5 is the second highest. The level of the optical signalreflected from the spaces of the data recording regions 6 is the thirdhighest, and the level of the optical signal reflected from the pre-pits12 formed in the header regions 5 is the lowest.

The recording pits 11 and the pre-pits 12 are formed so that, when thelight beams of the same level are irradiated on the header regions 5 andthe data recording regions 6, the amplitude of the level of the opticalsignal reflected from the header regions 5 (namely, the dynamic range ofthe optical signal reflected from the header regions 5) is equal to orlarger than the amplitude of the level of the optical signal reflectedfrom the data recording regions 6 (namely, the dynamic range of theoptical signal reflected from the data recording regions 6).

Such configuration allows the amplitude of the reproduction signalobtained from the header regions 5 to be sufficiently large. FIG. 7 isan example of the eye-pattern of the reproduced signals obtained fromthe header regions 5 and the data recording regions 6. The reproducedsignals are obtained by converting the optical signals reflected fromthe header regions 5 and the data recording regions 6 into electricsignals, cutting the direct current components of the electric signals,and extracting only the alternating current components. As indicated bythese eye-patterns, the amplitude of the reproduced signal obtained fromthe header regions 5 is sufficiently increased. The sufficiently largeamplitude of the reproduction signal obtained from the header regions 5improves the reliability in reading out the header information recordedin the header regions 5.

In order to increase the amplitude of the level of the optical signalreflected from the header regions 5 above the amplitude of the levels ofthe optical signal reflected from the data recording regions 6, thereflectances of the recording pits 11, the pre-pits 12, and the spacesare properly adjusted in the header regions 5 and the data recordingregions 6. The amplitude of the level of the optical signal reflectedfrom the header regions 5 depends on the reflectances of the pre-pits 12and the space in the header regions 5, and the amplitude of the level ofthe optical signal reflected from the data recording regions 6 dependson the reflectances of the recording pit 11 and the space in the datarecording regions 6. Therefore, adjusting the reflectances of therecording pits 11, the pre-pits 12 and the spaces in the header regions5 and the data recording regions 6 increases the amplitude of the levelof the optical signal reflected from the header regions 5 above theamplitude of the level of the optical signal reflected from the datarecording regions 6. The larger difference in between the reflectancesbetween the recording pits 11 and the spaces within the data recordingregions 6 is preferable for recording the user data onto the datarecording regions 6. However, in order to sufficiently increase theamplitude of the level of the optical signal reflected from the headerregions 5, it is important not to excessively decrease the reflectanceof the spaces of the data recording regions 6. If the reflectance of thespaces of the data recording regions 6 is excessively low, the amplitudeof the level of the optical signal reflected from the data recordingregions 6 becomes small. The reflectance of the space of the datarecording regions 6 needs to be properly selected on the basis of theamplitude of the level of the optical signal reflected from the datarecording regions 6. If a typical phase change material is used for therecording layer 2, the reflectance of the spaces in the data recordingregions 6 preferably ranges between 5 to 15%.

Alternatively, the amplitude of the level of the optical signalreflected from the header regions 5 may be increased above the amplitudeof the level of the optical signal reflected from the data recordingregions 6 through increasing the depth of the pre-pits 12 of the headerregions 5 to be larger than the depth of the pregroove 10 of the datarecording regions 6. The pregroove 10 is formed at the depth of about ⅛of the wavelength at which a push-pull signal used for detecting atracking error becomes maximum. In order to maximize the signalamplitude, the pre-pits 12 are formed so that the pre-pits 12 have adepth as close as possible to the depth of about ¼ of the wavelength.The optimization of the depth of the pre-pits 12 allows the reflectancein the pre-pits 12 to be substantially close to 0, and thereby enablesthe maximization of the amplitude of the level of the optical signalreflected from the header regions 5.

Second Embodiment

In a second embodiment, the recording pits 11 and the pre-pits 12 areformed such that a signal modulation degree of the header regions 5 islarger than a signal modulation degree of the data recording regions 6;the signal modulation degree of a certain region is the value obtainedby dividing the amplitude of the level of the optical signal reflectedfrom the region for the case that the pits and the space thatrespectively have the shortest pit length and the shortest space length,which are defined by a standard, are alternately arranged in thespecific region, by the amplitude of the optical signal level reflectedfrom the region for the case that the pits and the space thatrespectively have the longest pit length and the longest space length,which are defined by the standard, are alternately arranged in theregion. In general, the pit length and the space length are limited tospecific ranges when data is recorded in optical disks. For example, forthe 8/16 code, which is applied to DVDs, the shortest pit length isdefined as being 3T, and the longest pit length is defined as being 11T,where T is a pit length corresponding to a cycle of a channel clock. Thelimits of the pit length and the space length are required to reproducea clock from data recorded in an optical disk.

Alternately arranging the pits having the shortest pit length and thespaces having the shortest space length in a specific region involvesthat an optical signal having the highest repetition rate is reflectedfrom the region. Additionally, alternately arranging the pits having thelongest pit length and the spaces having the longest space length in aspecific region involves that an optical signal having the lowestrepetition rate is reflected from the region.

The arrangement of the pits and spaces for providing an optical signalwith the highest repetition rate minimizes the amplitude of the level ofthe reflected optical signal, while the arrangement of the pits andspaces for providing an optical signal with the lowest repetition ratemaximizes the amplitude of the level of the reflected optical signal.FIG. 8 is an eye-pattern of reproduced signals obtained from opticalsignals reflected from regions where pits and spaces having various pitlengths and space lengths are arranged. The ratio a/b between thesmallest amplitude of the reproduced signal, denoted by variable a, andthe largest amplitude of the reproduced signal, denoted by a,corresponds to the signal modulation degree of the region. The increasein the signal modulation degree increases the S/N ratio of thereproduction signal, and thereby enables data reproduction with highreliability.

The signal modulation degrees of the header regions 5 and the datarecording regions 6 are adjustable with the widths and lengths of therecording pits 11 and the pre-pits 12. Additionally, the signalmodulation degrees of the header regions 5 and the data recordingregions 6 are adjustable through differentiating the widths of therecording pits 11 and pre-pits 12 having short pit lengths from thewidths of the recording pits 11 and pre-pits 12 having long pit lengths.

When the optical disk in this embodiment is reproduced, which isdesigned so that the signal modulation degree of the header regions 5 islarger than the signal modulation degree of the data recording regions6, the gain of an amplifier for amplifying an electric signal outputtedfrom a pickup receiving the optical signals reflected from the headerregions 5 and the data recording regions 6 is adjusted so that theamplitudes of the reproduced signals obtained from the header regions 5and the data recording regions 6 are approximately constant. It would beeasily achieved with a relatively simple circuitry to adjust the gain sothat the amplitudes of the reproduction signals obtained from the headerregions 5 and the data recording regions 6 are controlled to beapproximately constant. The reliability in reading out the headerinformation recorded in the header regions 5 is improved throughincreasing the signal modulation degree of the header regions 5 underthe conditions that the amplitudes of the reproduction signals obtainedfrom the header regions 5 and the data recording regions 6 arecontrolled to be approximately constant.

The linear recording density of the header regions 5 may be set to belower than the linear recording density of the data recording regions 6in order to increase the signal modulation degree of the header regions5 above the signal modulation degree of the data recording regions 6.The signal modulation degree is increased as the increase in the linearrecording density when the same encoding method is used in the headerregions 5 and the data recording regions 6. Decreasing the linearrecording density of the header regions 5 below the linear recordingdensity of the data recording regions 6 is preferable, because thismakes it easy to increase the signal modulation degree of the headerregions 5 above the signal modulation degree of the data recordingregions 6.

When the channel clock is reproduced from the data recorded in theoptical disk, the fact that the record line density of the headerregions 5 and the record line density of the data recording regions 6are different brings about a new problem that the cycles of the channelclocks are different between those regions. When the cycle of thechannel clock of the data recording region 6 differs from that of theheader regions 5, the time while no data is reproduced may be observedupon switching the region where the data is reproduced from the headerregions 5 to the data recording regions 6. Similarly, when the cycle ofthe channel clock of the header regions 5 differs from that of the datarecording regions 6, the time while no data is reproduced may beobserved upon switching the region where the data is reproduced from thedata recording regions 6 to the header regions 5. This is because thedifference in the cycle of the channel clock may necessitate the timefor establishing the synchronization of the clocks.

In order to avoid the desynchronization of the clock, the cycle of thechannel clock reproduced from the header regions 5 is set to be integertimes as long as the cycle of the channel clock reproduced from the datarecording regions 6. That is, the cycle of the channel clock reproducedfrom the header regions 5 is set to nT, where T is the cycle of thechannel clock reproduced from the data recording regions 6, and n is theinteger of 2 or more. In order to minimize the difference of the cyclesof the channel clocks, the cycle of the channel clock reproduced fromthe header regions 5 is set to 2T.

The data reproduction is achieved without desynchronization throughsetting the cycle of the channel clock reproduced from the headerregions 5 to be the integer times as long as the cycle of the channelclock reproduced from the data recording regions 6.

The cycle of the channel clock reproduced from the header regions 5 andthe cycle of the channel clock reproduced from the data recordingregions 6 may be adjusted so as to satisfy the above-mentioned conditionon the basis of the arrangement of the pre-pits 12 of the header regions5 and the arrangement of the recording pit 11 of the data recordingregions 6, respectively.

Additionally, for the case when a wobble groove is used as the pregroove10 of the data recording regions 6, the wobbling cycle of the wobblegroove may be adjusted so that the cycle of the channel clock reproducedfrom the data recording regions 6 satisfies the above-mentionedcondition. The wobble groove is wobbled at a cycle corresponding to thecycle of the channel clock multiplied by an integer, and the channelclock is reproduced from the wobbled wobble groove. In this case,adjusting the wobbling cycle of the pregroove 10 formed in the datarecording regions 6 so that the wobbling cycle corresponds to the cycleof the channel clock of the header regions allows the data recorded inboth of the header regions 5 and the data recording regions 6 to bereproduced by using the clock reproduced from the pregroove 10.

Third Embodiment

In a third embodiment, as shown in FIG. 9, long pre-pits (recognitionpits 7) are formed at the head of the header regions 5 so that a drivercan surely detect the header regions 5. The recognition pits 7 areembossed, and thus the reflectance of the recognition pits 7 are lowerthan the reflectance of the spaces of the data recording regions 6, asis the case of the pre-pits 11.

Conventionally, the highly reflective spaces having a predeterminedlength are formed in the header regions of optical disks, and the diskdrives find the header regions through detecting the highly reflectivespaces. In optical disks where highly reflective recording pits areformed, however, the reflectance of the spaces is not always thehighest. Thus, this method cannot be applied to optical disks where thehighly reflective recording pits are formed.

For this reason, in the third embodiment, the long recognition pits 7are formed at the head of the header regions 5, and the recognition pits7 are used to recognize the header regions 5.

The recognition pits 7 have a length longer than the longest pit lengthdefined by the standard used for coding data to be recorded in the datarecording regions 6. The fact that the recognition pits 7 are longerthan the longest pit length enables the recognition pits 7 to bedistinguished from the pits representing the data. Reproducing data fromthe header regions 5 including the long recognition pits 7, as shown inFIG. 9, allows the reproduced signal to have a reduced level associatedwith the recognition pits 7 for a time period Al of a certain duration.This facilitates the recognition of the header regions 5.

The optical disks of the first to third embodiments are reproduciblewith a disk drive composed of a commonly used signal reproducingcircuit. In order to further improve the reliability of the reproductionof the header information, the characteristics of the signal reproducingcircuit used to reproduce the header information recorded in the headerregions 5 is preferably different from the characteristics of the signalreproducing circuit used to reproduce the data recorded in the datarecording regions 6. It would be preferable that the characteristics ofthe signal reproducing circuit of the disk drive is properly adjusted onthe basis of the difference between the reproduction signal amplitudesobtained from the header regions 5 and the data recording regions 6, thedifference between the signal modulation degrees and the differencebetween the cycles of the channel clocks. The optimization of thecharacteristics of the signal reproducing circuit accompanied by theimprovement of the property of the optical disk further improves thereliability of the reproduction of the header information.

Although the present invention has been explained above with referenceto the various embodiments, it does not intend that the presentinvention is limited to these embodiments. Those skilled in the artwould appreciate that changes may be allowed within the spirit of thepresent invention.

For example, the recording track is not always formed only inside thepre-groove; the recording tracks may be formed in both of the groovesand the lands between these grooves.

FIGS. 10 to 12 illustrate modifications of the third embodiment, inwhich the recording tracks are formed in both of the groove and theland. As shown in FIGS. 10 and 11, the pre-pits 12 formed in the headerregions 5 of the land recording track may be displaced from the pre-pits12 formed in the header regions 5 of the groove recording track. This iseffective for avoiding interference between the adjacent recordingtracks. The recognition pits 7 may be arranged at the head of the headerregions 5, as shown in FIG. 10. Alternatively, as shown in FIG. 11, therecognition pits 7 may be arranged at the head of the pre-pits 12representing the header information.

Moreover, as shown in FIG. 12, the pre-pits 12 indicating the headerinformation may be formed so as to overlap with a pair of a landrecording track and a groove recording track. In this case, the headerinformation is commonly used in the land recording track and the grooverecording track. When the pre-pits 12 overlap with the land recordingtrack and the groove recording track, the recognition pits 7 may be alsoformed so as to overlap with the land recording track and the grooverecording track. The recognition pits 7 may be formed for each recordingtrack, and the pre-pits 12, indicating the header information, may beformed so as to overlap with the land recording track and the grooverecording track.

Also, those skilled in the art would appreciate that the header region 5in a certain pair of a land recording track and a groove recording trackmay be displaced from the header region 5 in another pair of a landrecording track and a groove recording track.

Moreover, those skilled in the art would appreciate that the pre-pitsmay be discretely formed in the land provided beside the grooverecording track, as is the case for DVD-Rs. When the pre-pits are formedat the portion other than the center of the recording track, the headerinformation may be read out on the basis of the change in the push-pullsignal in place of the change in the reflected optical signal. In thiscase, the present invention may be applied with regard to the amplitudesof the levels of the optical signals received by the two opticaldetectors generating the push-pull signal.

Moreover, the recording data may be multiplexedly written onto theheader regions where the pre-pits are formed. The present inventionapplies to this configuration. When the recording pits are formed in theheader regions, the effective signal can be detected from a pre-pitreproduction signal obtained from the spaces between the recording pitsand the like.

Although the above-mentioned explanations assume that short headerregions are cyclically formed in the recording track, the header regionsmay be collectively formed in the inner circumference region of theoptical disk, which is the leading portion of the recording track on theentire optical disk. In this case, the header regions may be removedfrom the recording tracks except the inner circumference region.Instead, short header regions containing the address information, whichis minimumly required, may be cyclically left.

As thus described, even if the header regions are collectively formed inthe inner circumference portion, this portion is covered with therecording medium having a reduced reflectance; therefore, applying thepresent invention enables the stable information reproduction.

1. An optical disk comprising: a recording track including: data recording regions where recording pits are formed for recording data; and header regions where pre-pits are formed for recording header information identifying said data recording regions, wherein said recording pits have a reflectance larger than that of a space, where said recording pits are not formed, wherein said recording pits and said pre-pits are formed such that, when optical beams having the same intensity are irradiated on said data recording regions and said header regions, an amplitude of a level of an optical signal reflected by said header regions is one of equal to and greater than that of a level of an optical signal reflected by said data recording regions, wherein the recording pits formed in the data recording regions have a highest reflectance, wherein said space in the header regions have a second highest reflectance, wherein said space in the data recording regions have a third highest reflectance, and wherein said pre-pits formed in the header regions have a lowest reflectance.
 2. The optical disk according to claim 1, wherein said data recording regions include a pregroove in which said recording pits are formed, and a depth of said pit-pits is deeper than that of said pregroove.
 3. The optical disk according to claim 2, wherein said depth of said pre-pits is twice as deep as that of said pregroove.
 4. The optical disk according to claim 1, wherein said header regions are collectively formed in a leading portion of said recording track disposed in an inner circumference region of said optical disk.
 5. An optical disk comprising: a recording track including: data recording regions where recording pits are formed for recording data; and header regions where pit-pits are formed for recording header information identifying said data recording regions, wherein said recording pits have a reflectance larger than that of a space, where said recording pits are not formed, wherein said recording pits and said pre-pits are formed such that a signal modulation degree of said header regions is greater than that of said data recording regions, wherein the recording pits formed in the data recording regions have a highest reflectance, wherein said space in the header regions have a second highest reflectance, wherein said space in the data recording regions have a third highest reflectance, and wherein said pre-pits formed in the header regions have a lowest reflectance.
 6. The optical disk according to claim 5, wherein a linear recording density of said header regions is lower than that of said data recording regions.
 7. The optical disk according to claim 6, wherein said recording pits and said pre-pits are formed such that a cycle of a channel clock reproduced from said header regions is n-times as long as that of a channel clock reproduced from said data recording regions, n being an integer one of equal to and greater than
 2. 8. The optical disk according to claim 6, wherein said data recording regions include a wobble groove in which said recording pits are formed, and wherein said pre-pits and said wobble groove are formed such that a cycle of a channel clock reproduced from said header regions is n-times as long as that of a channel clock reproduced from said data recording regions, n being an integer one of equal to and greater than
 2. 9. The optical disk according to claim 5, wherein said header regions are collectively formed in a leading portion of said recording track disposed in an inner circumference region of said optical disk.
 10. An optical disk comprising: a recording track including: data recording regions where recording pits are formed for recording data; and header regions where pre-pits are formed for recording header information identifying said data recording regions, wherein said recording pits have a reflectance larger than that of a space, where said recording pits are not formed, wherein one of said pit-pits which is located closest to a head of said header regions has a longer length than the maximum pit length defined by a standard for coding said data, wherein the recording pits formed in the data recording regions have a highest reflectance, wherein, said space in the header regions have a second highest reflectance, wherein said space in the data recording regions have a third highest reflectance, and wherein said pre-pits formed in the header regions have a lowest reflectance.
 11. An optical disk reading method comprising: providing a drive including a signal reproducing circuit with an optical disk including: a recording track comprising: data recording regions comprising recording pits formed for recording data, said recording pits having a reflectance larger than that of a space, where said recording pits are not formed; and header regions comprising pre-pits formed for recording header information identifying said data recording regions, said recording pits and said pre-pits being formed such that, when optical beams having the same intensity are irradiated on said data recording regions and said header regions, an amplitude of a level of an optical signal reflected by said header regions is one of equal to and greater than that of a level of an optical signal reflected by said data recording regions; and configuring characteristics of said signal reproducing circuit for reading said header information recorded in said header regions such that said configured characteristics are different from characteristics used for reading data recorded in said data recording regions, wherein the recording pits formed in the data recording regions have a highest reflectance, wherein said space in the header regions have a second highest reflectance, wherein said space in the data recording regions have a third highest reflectance, and wherein said pre-pits formed in the header regions have a lowest reflectance.
 12. An optical disk reading method comprising: providing a drive including a signal reproducing circuit with an optical disk including: a recording track comprising: data recording regions comprising recording pits formed for recording data, said recording pits having a reflectance larger than that of a space, where said recording pits are not formed; and header regions comprising pre-pits formed for recording header information identifying said data recording regions, said recording pits and said pre-pits being formed such that a signal modulation degree of said header regions is greater than that of said data recording regions; and configuring characteristics of said signal reproducing circuit for reading said header information recorded in said header regions such that said configured characteristics are different from characteristics used for reading data recorded in said data recording regions, wherein the recording pits formed in the data recording regions have a highest reflectance, wherein said space in the header regions have a second highest reflectance, wherein said space in the data recording regions have a third highest reflectance, and wherein said pre-pits formed in the header regions have a lowest reflectance.
 13. An optical disk reading method comprising: providing a drive including a signal reproducing circuit with an optical disk including: a recording track including: data recording regions comprising recording pits formed for recording data, said recording pits having a reflectance larger than that of a space, where said recording pits are not formed; and header regions comprising pre-pits formed for recording header information identifying said data recording regions, wherein one of said pre-pits which is located closest to a head of said header regions has a longer length than the maximum pit length defined by a standard for coding said data; and configuring characteristics of said signal reproducing circuit for reading said header information recorded in said header regions such that said configured characteristics are different from characteristics used for reading data recorded in said data recording regions, wherein the recording pits formed in the data recording regions have a highest reflectance, wherein said space in the header regions have a second highest reflectance, wherein said space in the data recording regions have a third highest reflectance, and wherein said pre-pits formed in the header regions have a lowest reflectance. 